1. Field of the Invention
The present invention relates generally to a method and to an arrangement for echo compensation in which a filter is provided whose filter coefficients are controlled depending upon the echo signal.
2. Description of the Related Art
Echo compensators are used in signal connections, such as in speech connections which have a long run time. The purpose of echo compensators is to compensate for disturbing signals which are called echo signals and are caused by transmission signals. The echo signals are due to incomplete decoupling of the transmission paths, such as at a terminal hybrid or at reflection points of the transmitter of a connected two-wire line.
In an echo compensator, the echo signal is emulated from the transmission signal by a filter arrangement and is then subtracted from the reception signal which is made up of the desired reception signal and an echo signal.
Higher demands are being made on echo compensators and so adaptive digital filters such as FIR filters are used which have adjustable coefficients. An echo compensator using an adjustable coefficient is disclosed in, for example, "Kleinheubacher Berichten" 26, 1983 of the Central Office for Communication Technology in Darmstadt, pp. 427-435.
On one hand, echo compensators should adjust themselves rapidly and precisely to the echo signal and, on the other hand, echo compensators should hold their setting in a stable manner when speech signals are superimposed on the echo signal such as in the case of simultaneous cross talk. Problems are a cause by loud environmental noises which are also superimposed on the echo signal. The echo compensator must be able to adjust itself despite these loud environmental noises. For a rapid adjustment, the filter coefficients must change quickly and be able to change with large increments but, on the other hand, for a precise setting which is not sensitive to noise, the filter compensation must necessarily be finely stepped.